Temperature monitor and limit
The LTC3626 produces an estimate of the on-die temperature at the TMON pin. This feature can be used to determine the quality of the ground connection to the QFN exposed pad made during assembly. The exposed pad for the QFN is intended to provide a low impedance electrical connection to the board as well as good thermal contact. Visual inspection of this critical connection can be difficult, and a poor exposed pad connection may not be apparent by simple observation of the regulated output voltage even though the on-die temperature may be far too high for reliable, long-term part operation. Measurement of the TMON pin however gives the user insight into the exposed pad connection and hence the internal part operating environment.
As an example, Figure 5
shows data taken on two parts, one with a good exposed pad connection to the PCB, the other with a poor exposed pad connection. Though both parts regulate to the expected output voltage, it is clear from the internal temperature measurement that the internal operating environment is very different between the two parts. If placed in a system with an ambient operating temperature of say 70°C, the device with the poor exposed pad connection will clearly exceed the maximum allowed junction temperature of 125°C and will thus have compromised long-term reliability.
Figure 5: It is easy to determine the quality of the exposed pad connection by examining temperature measurements made by the LTC3626.
The continuous push for higher performance and power density faced by today’s system designers require small, flexible, and efficient point-of-load converters to maximize overall power chain efficiency. The LTC3626’s combination of wide input voltage range, output current capability, flexible feature set, and very small form factor make it suitable for many of today’s point-of-load regulator applications.
About the author
Keith Bassett is design engineering section leader at Linear Technology Corp.
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